Japanese Patent Laying-Open No. 2-266855 discloses a starter-generator attaining a function as a three-phase motor starting an engine mounted on a vehicle and a function as a three-phase AC generator charging a battery.
Referring to FIG. 14, a starter-generator 300 disclosed in Japanese Patent Laying-Open No. 2-266855 includes a motor unit 301 and a drive unit 302. Motor unit 301 includes a stator and a rotor. Drive unit 302 is provided on an end surface 301A of motor unit 301. Drive unit 302 includes a cylindrical member 302A and a power module 302B. Power module 302B is formed on a surface of cylindrical member 302A. That is, power module 302B is arranged in a direction perpendicular to a radial direction 303 of cylindrical member 302A and in a longitudinal direction 304 of a rotation shaft 301B of motor unit 301.
Power module 302B feeds a current to a coil included in motor unit 301 and drives motor unit 301 so that the rotor outputs a prescribed torque. When the rotor in motor unit 301 rotates by rotation power of an engine, an AC voltage induced in three stators is converted to a DC voltage, whereby a battery is charged.
In this manner, power module 302B is provided on end surface 301A of motor unit 301, and drives motor unit 301 as a motor or a generator.
Japanese Patent Laying-Open No. 63-202255 discloses a starter-charger starting an engine mounted on a vehicle and charging a battery. FIG. 15 is a circuit diagram of the starter-charger disclosed in Japanese Patent Laying-Open No. 63-202255. Referring to FIG. 15, a starter-charger 400 includes a battery 310, a key switch 320, a voltage regulator 330, a field coil 340, a crank angle detector 350, an armature current switching circuit 360, and an armature coil 380.
Battery 310 outputs a DC voltage. Key switch 320 is connected to an e terminal side at the time of start of the engine (not shown), and connected to a d terminal side after the start of the engine.
Voltage regulator 330 includes resistors 331 to 333, a Zener diode 334, transistors 335, 337, and a flywheel diode 336. Resistors 331, 332 are connected in series between a positive bus PLE of battery 310 and a ground node GND.
Resistor 333 and transistor 335 are connected in series between the d terminal of key switch 320 and ground node GND. Transistor 335 has the collector connected to resistor 333 and the base of transistor 337, the emitter connected to ground node GND, and the base connected to Zener diode 334.
Zener diode 334 is connected between a node N1 and the base of transistor 335. Flywheel diode 336 and transistor 337 are connected in series between positive bus PLE and ground node GND. Transistor 337 has the collector connected to one end of field coil 340, the emitter connected to ground node GND, and the base connected to the collector of transistor 335.
Flywheel diode 336 absorbs surge produced when transistor 337 opens or closes.
Field coil 340 has one end connected to the collector of transistor 337 and the other end connected to positive bus PLE of battery 310.
With such a circuit configuration, voltage regulator 330 detects a DC voltage output from battery 310 in a power generation state, and regulates a field current flowing through field coil 340 in order to maintain a voltage value of the detected DC voltage at a prescribed value.
Crank angle detector 350 detects a crank angle between respective phases of armature coil 380, and outputs the detected crank angle to armature current switching circuit 360.
Armature current switching circuit 360 includes a current switch control circuit 361, N-type MOS transistors 362 to 367, and Zener diodes 368 to 373. Current switch control circuit 361 is connected to the e terminal of key switch 320, and receives a crank angle from crank angle detector 350. Current switch control circuit 361 is driven by the DC voltage from the e terminal so as to generate a signal to turn on/off N-type MOS transistors 362 to 367 based on the crank angle, and outputs the generated signal to each of N-type MOS transistors 362 to 367.
N-type MOS transistors 362, 363 are connected in series between positive bus PLE and ground node GND. N-type MOS transistors 364, 365 are connected in series between positive bus PLE and ground node GND. N-type MOS transistors 366, 367 are connected in series between positive bus PLE and ground node GND.
N-type MOS transistors 362, 363 are connected between positive bus PLE and ground node GND, in parallel to N-type MOS transistors 364, 365 and N-type MOS transistors 366, 367. In addition, N-type MOS transistors 362, 364, 366 have respective drain terminals connected to positive bus PLE, and have source terminals connected to the drain terminals of N-type MOS transistors 363, 365, 367 respectively. Moreover, N-type MOS transistors 363, 365, 367 have the drain terminals connected to source terminals of N-type MOS transistors 362, 364, 366 respectively, and have respective source terminals connected to ground node GND.
A node N2 between N-type MOS transistor 362 and N-type MOS transistor 363, a node N3 between N-type MOS transistor 364 and N-type MOS transistor 365, and a node N4 between N-type MOS transistor 366 and N-type MOS transistor 367 are connected to different phases of armature coil 380 respectively.
Zener diode 368 is connected in parallel to N-type MOS transistor 362, between positive bus PLE and node N2. Zener diode 369 is connected in parallel to N-type MOS transistor 363, between node N2 and ground node GND.
Zener diode 370 is connected in parallel to N-type MOS transistor 364, between positive bus PLE and node N3. Zener diode 371 is connected in parallel to N-type MOS transistor 365, between node N3 and ground node GND.
Zener diode 372 is connected in parallel to N-type MOS transistor 366, between positive bus PLE and node N4. Zener diode 373 is connected in parallel to N-type MOS transistor 367, between node N4 and ground node GND.
With such a circuit configuration, armature current switching circuit 360 switches a DC current flowing from battery 310 to armature coil 380.
When the engine is started, key switch 320 is connected to the e terminal. Armature current switching circuit 360 turns on/off N-type MOS transistors 362 to 367 based on the crank angle from crank angle detector 350 and switches the DC current flowing from battery 310 to armature coil 380, so as to start the engine.
After the engine is started, key switch 320 is connected to the d terminal, and N-type MOS transistors 362 to 367 are all turned off. Starter-charger 300 operates as a generator, and voltage regulator 330 regulates a current fed to field coil 340 in order to set a voltage value of the DC voltage from battery 310 to a prescribed value. Electric power generated by armature coil 380 is DC-converted by Zener diodes 368 to 373 for charging battery 310.
In this manner, starter-charger 300 drives the engine in starting the engine, and operates as a generator after the engine is started. Even if surge produced in cutting off load or surge produced in an ignition system of the engine is applied to armature current switching circuit 360, the applied surge flows through Zener diodes 368 to 373. Therefore, N-type MOS transistors 362 to 367 are protected by Zener diodes 368 to 373.
In the conventional starter-generator, however, the power module is arranged in a direction perpendicular to a radial direction when the rotation shaft is assumed as a center and in a longitudinal direction of the rotation shaft. Accordingly, it is difficult to achieve a smaller size of the control circuit controlling drive of the motor.
In addition, the conventional starter-generator has not been able to sufficiently cool the power module.
Moreover, in the conventional starter-charger, the control circuit driving a motor including the field coil and the armature coil includes six switching elements and six Zener diodes provided corresponding to six switching elements. Accordingly, if the control circuit driving the motor is provided at an end portion of an alternator, an overall size of the control circuit cannot be made smaller.